When it was developed the K&N Filtercharger was an air filtration breakthrough and it still has the edge today...

K&N's simple, economical high-performance air filters improve acceleration and add about 1 to 4 horsepower to your engine. Each OE-style air filter provides virtually unrestricted airflow with exceptional filtration that is designed to last the life of an engine. High-performance OE filters are made of 4 to 6 sheets of high-flow cotton gauze layered between 2 aluminum wire mesh sheets that are pleated and oiled to enhance filtering and overall performance. OE-style replacement air filters are washable, reusable, and environmentally-friendly; allowing you to drive up to 50,000 miles before filter cleaning is required (depends on driving conditions)